According to the Oxford English Dictionary, Real Ale is "a name for draft (or bottled) beer brewed from traditional ingredients, matured by secondary fermentation in the container from which it is dispensed, and served without the use of extraneous carbon dioxide."

The is below is correct,if a little oxford. Basicly yeast is added to the "container" so that the beer continues to be live ie improve with age. Two basic types; cask and bottle conditioned.Cask will see a hand pull/pump used for dispence rather than a font,bottle condioned will need careful lable reading to identify if you dont know the brand.although there is now a "CAMRA says this real ale" labling scheme starting to appear,to help the uninitiated.